This invention relates to a press with knee or toggle joint drive mechanisms of the type including a press frame and a press ram guidably supported for linear movement at the press frame. A plurality of toggle joint drive mechanisms are provided, each of which include a drive member, a first link member, and a second link member, the first link member having one portion thereof pivotally connected to a ram coupling point of the press ram and another portion thereof pivotally connected to a first coupling point of the drive member. The second link member has a portion thereof pivotally connected to a frame coupling point of the press frame and a second portion thereof pivotally connected to a second coupling point of the drive member at a position spaced from and facing the first coupling point. Rotatable drive crankshaft means are provided for applying driving forces to the drive member.
U.S. Pat. No. 2,085,648 is exemplary of prior art presses with such toggle joint drive mechanisms. Each knee or toggle joint drive mechanism consists of two links (arms, stilts), wherein one link is hingedly joined with one end to a power transmission member or a press ram in a ram hinge or coupling point and with the other end to the second link. The second link is fashioned as a rocking lever and is rotatably mounted in a frame coupling point. While one rocker arm of the second link is connected to the link hingedly joined in the ram coupling point, a drive member engages the second link, which drive member is eccentrically supported on a gear wheel. The gear wheel proper is supported on an axle disposed symmetrically with respect to the toggle lever drives. The gear wheels associated with the further toggle joint drive mechanisms are also disposed on this axle, so that a symmetrical structure can be realized. In case of a press constructed with the aforementioned toggle joint drive mechanisms with several pressure points, however, only an almost symmetrical motion operation of a ram and/or of a blank holder can be achieved, as seen over a rotation of the crankshaft.
In many cases of application of a press, it is desirable to attain a nonsymmetrical motion operation, in such a way that a crankshaft rotation of the press drive mechanism is subdivided into a ram motion with an initial phase and a final phase with high speed and a relatively long path and an interposed operating phase with an almost constant, low velocity and a relatively small path.
The very old German Pat. No. 38,701 suggested, for the drive mechanism of a blank holder, to construct a toggle joint drive mechanism with a triangular guide means wherein the corner of the triangular guide means forming an acute angle is eccentrically joined to drive means, while the two corners facing away from the acute angle are connected to mutually facing ends of two links. The ends of the links which face away from each other are hingedly connected, on the one hand, to a blank holder and, on the other hand, in the extension of the travel path of the blank holder to a press frame.
More recent solutions of the aforementioned requirement for a nonsymmetrical operation of a press ram and/or of a blank holder disclose complicated joint drive mechanisms for presses with a pressure point, such as they are described, for example, in the technical book "Die Mechanischen Pressen" (The Mechanical Presses) by Heinrich Makelt, published by Carl Hanser Verlag, Munich, 1961, p. 88, and German Published Application No. (DOS) 2,000,669.
This invention is based on the problem of avoiding the conventional, complicated, and troublesome drive mechanisms and of applying certain aspects of a previously contemplated drive mechanism for a blank holder, together with its advantages, to a drive mechanism for a press and with toggle joint drive mechanisms engaging several pressure points of the press ram, in order to obtain a nonsymmetrical motion operation of the press ram during a rotation of the crankshaft.
According to preferred embodiments of the present invention, the above-mentioned problems and disadvantages are avoided by a press of the above-described type by providing that each drive member is an acute-angled triangular guide member having the acute angle corner thereof (smallest angle corner) connected to the drive means for movement therewith, and with said first and second coupling points for the link members being at the other respective corners of the guide member.
According to certain preferred embodiments of the present invention, each press ram is provided with four pressure points at which respective link members of four respective separate toggle joint drive mechanisms are connected, with said four coupling points at the press ram being disposed to impart symmetrical application of force on the press ram.
According to other preferred embodiments of the present invention, the press ram is connected hingedly to the link members only at two pressure points. In order to obtain symmetrical application of forces with two pressure points, three separate triangular shaped guide members are provided. A first and second of these guide members are disposed axially externally of the third guide member. The third guide member is connected to the link members for one of the pressure points. On the other hand, the first and second guide members are interconnected with one another at the respective corners opposite the smallest angle acute angle by way of pin members. These pin members in turn are articulated to respective link members attached to the frame and the press ram, with the attachment at the press ram being in the same plane, along the length of the axis of the rotational shaft for driving the guide members, as is the connection of the third guide member link member to the press ram.
The preferred embodiments of the present invention are very advantageous with respect to the small number of moving parts required, the provision of a central drive shaft from which movements of all the toggle joint drive mechanisms can be easily obtained in a symmetrical force applying manner at the press ram, and in the simplified arrangement for converting the rotation of the crankshaft to the respective opposite rotation of the symmetrically disposed toggle joint drive mechanism to effect the linear movement of the press ram.